The present invention is directed generally to an improved method for communicating a wheel speed sensor fault in an anti-lock braking system (ABS) for a road vehicle having a warning light.
Warning light activation in an ABS is generally described in German Patent A1 4106704. In such prior art, the ABS fault lamp or warning light turns on when the vehicle ignition is turned on. Thereupon, the wiring of the ABS and other hardware are tested. If this test does not detect any faults, the fault lamp goes out, otherwise it remains on and the fault is stored in a fault memory of the ABS.
Thereafter, while the vehicle is moving, i.e., when the vehicle speed is greater than a limit speed, the wheel speed sensors are checked for correct function and voltage output. If this check does not detect any faults, the fault lamp remains off. If a fault is detected, however, the light goes on again and the fault is stored in a fault memory of the ABS. The same procedure takes place for other faults recognized during driving, including hardware faults and loose contacts.
If an old sensor fault, i.e., a fault from a previous operating cycle, is still stored in the ABS electronics when the vehicle is started, the fault lamp remains on after the wiring test. Now, the result of the actual sensor test conducted when the vehicle is being driven is awaited. If, now, the sensor in question is recognized to be fault free on this occasion, the fault lamp goes out and the fault memory in question is cleared.
The prior art ABS described above is commonly available in two versions as regards its voltage supply.
In one version, the voltage supply is turned on and off with the ignition switch of the vehicle. In this case, the ABS is functional during the entire operating time of the vehicle (permanent supply).
In the other version, the brake light switch of the vehicle controls (directly or indirectly) the voltage supply. In this case, the ABS is in operation only when the driver has depressed the brake pedal, whereupon the ABS performs its function of monitoring and, if necessary, regulating the braking action.
Anti-lock braking systems of the latter version therefore have much smaller current consumption. Indeed, they do not consume any current while the vehicle is stationary with the ignition turned on. Moreover, if such systems are disposed in trailers, they do not need their own power supply lines from the towing vehicles. However, fault recognition in such systems with brake light supply is more difficult, especially for the wheel speed sensors, since they are energized only briefly, namely during braking, and it is only then that they are able to be tested for faults.
Generally speaking, in accordance with the present invention, an improved method for communicating a wheel speed sensor fault in a vehicle ABS is provided which overcomes disadvantages associated with prior art methods.
The method according to the present invention is carried out in a conventional vehicle ABS (including in an ABS in which voltage supply is controlled by the brake light switch) having wheel speed sensors for monitoring the speed of the vehicle wheels, a warning light and a fault memory for storing sensor fault bits. In such an ABS, the warning light is actuated and a sensor fault bit is set in fault memory when a wheel speed sensor is recognized as faulty with respect to its voltage signal. The warning light is deactivated and the fault bit is deleted from memory when the wheel speed sensor has been recognized as fault free.
The method according to the present invention improves over such conventional systems by deactivating the warning light and deleting the associated fault bit from fault memory when the voltage signal previously recognized as faulty is higher than a predefined voltage threshold when the vehicle is moving at a predefined low limit speed.
Accordingly, it is an object of the present invention to provide a method for communicating a wheel speed sensor fault in an ABS, and for checking the function of the wheel speed sensors in the ABS, whereby a fault of a wheel speed sensor will be accurately signaled to the driver of the vehicle.
Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification.
The present invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and embodies features of construction, combination of elements, and arrangement of parts which are adapted to effect such steps, all as exemplified in the detailed disclosure hereinafter set forth, and the scope of the invention will be indicated in the claims.